Covers of this kind which give a quick closure by means of a bayonet joint, are known for numerous applications, for example, for oil tanks, the cooling water containers of a motor vehicle and the like. Cover locking devices are carried inside the cover designed for specific tanks. By a slight rotation of the cover, usually assisted by a suitable downward pressure, the locking elements of such devices are guided by a curved bayonet track ridge internally of the tank neck and generally stopped from rotation after a quarter turn.
A spring tension arrangement provides for a prestressing of the locking elements and a reliable guiding and a clamping of the cover to the tank. A sealing, with a ventilating drilled hole, if applicable, can be obtained by means of an additional seal.
Known covers consist of several parts, specifically, the actual cover, the inner part with the locking elements and a spring means, generally a spiral spring, for producing the desired prestress. Furthermore, the cover usually also has a member to be inserted as an outer support for the spiral spring.
Since the sheet metal part in the known constructions constitutes a rigid element with the locking elements, the spring had the task of bringing about a tolerance adjustment along with the prestressing and sealing of the cover.